Storage Migration Service experience

I decided to give the storage migration service a try but I'm going to end up abandoning it and going back to robocopy because it kind of sucks, is a pain to use and doesnt have the features I ended up needing.  I wanted to list some of those pain points so maybe you could take them into account in future releases.

1. Performance sucks The source server i was using had 1.5 TB of data and it took 5 hours to inventory.  Blindly robocopying all the data takes half the time.  I didnt even get to the actual copy phase, so I dont even know how bad that would have been.  The source server hardware sucks, so thats a good part of why things are slow, but its not as fast as just using robocopy.
2. Worthless error messages After the inventory was complete, there were some shares with the error "Couldn't inventory some devices".  Thats beyond useless and makes no sense in the context.  What is the "device" being inventoried?  It couldnt have been the disk because all these shares, some of which inventoried fine, are on the same disk.  Did you mean some files couldnt be inventoried?  That would make sense but then i'd also expect a list of failed files that I could look over to either remediate or ignore the issue.  
3. Cant select source files For some reason I'm forced to inventory all shares on a given disk.  This wastes time since I'm only interested in a specific share/folder.  Additionally, some of the shares on this source server are sub shares of other shares which leads to the inventory process scanning the same content multiple times.  Further decreasing performance.  You should both allow the selection of individual shares, or better yet, individual folders AND make sure the service is smart enough to not duplicate inventory.  I think the idea of using shares as the inventory source instead of disk content is a mistake.  Instead of inventorying shares you should inventory disk content and then flag what parts of that content are shared.  Additionally when adding a source server, the next step should be selecting which folders on the disk you want to inventory.  Default can be everything, with the option of a standard folder hierarchy from which you can select individual folders/subfolders. 
4. Cant map destination folders I wanted to map the source folder to a different destination folder, and there doesnt appear to by any way to do this.  Instead it looks like its just going to create the same folder.  This is where I gave up because it turns out this just wont do what I need.  

I think you need to go back to the drawing board on this one.  Maybe look at robocopy and use it as the design basis.  I was kind of excited when I read the docs on storage migration service, but the reality is its not as flexible or functional as I need.